WASHINGTON
— THE Middle East peace process may finally be lurching forward - but when it comes to United States arms exports, Israel remains a preferred customer.

That is a signal the Clinton administration sent this week by dangling a sale of modified F-15E warplanes in front of Israeli Prime Minister Yitzhak Rabin. The Strike Eagle F-15E model is among the fanciest attack jets in the Air Force arsenal. The version Israel might buy would be the most capable warplane ever exported by US manufacturers.

It would, for instance, have greater ground-attack capability than the 72 F-15FXs the US last year agreed to sell Saudi Arabia.

The 20 jets Israel wants would be worth just shy of $2 billion. Officially, the Israelis have made no decision between the F-15E variant and other US products, such as the F-16 or F-18. But Pentagon officials said the F-15 was a leading candidate.

Paying for the plane remains a problem. Even with a long-term schedule, payments would take large chunks of the $1.8 billion in annual US aid to Israel. ``I hope that by the end of this week, or later, a decision will be made,'' Mr. Rabin said Nov. 15, after meeting with Secretary of Defense Les Aspin for three hours. Arab reaction unknown

How Arab nations will react to the prospect of a big arms sale to Israel during peace negotiations remains to be seen. But Clinton officials insist that unless Israel feels that it can retain its regional military edge, it will not feel secure enough to make needed negotiation concessions.

The F-15E's attraction - in its stripped-down Israeli version, it would be dubbed the F-15I - is its ability to drop precision-guided weapons at great ranges, at night or in bad weather.

While Israeli Air Force F-16s have some limited deep-strike capability, they can only reach about halfway into, say, Iraq. Yet Iran's developing Scud ground-to-ground missile capability, as well as worry about Saddam Hussein, are legitimate Israeli concerns, one expert argues.

Israel is ``going to have to develop the capability to strike deeper than ever before,'' says Michael Eisenstadt, a military analyst at the Washington Institute for Near East Policy. ``The F-15E is going to be the only platform to give them this kind of ability.''

Israeli desire for the Strike Eagle stems from the Gulf war, he says, when US F-15Es were used to hit targets deep inside Iraq with impunity. The only more capable US tactical platform is the F-117 Stealth fighter, which was produced in a limited production run and is unlikely to be exported in the near future.

Israel already has 51 older-model F-15s outfitted more as traditional air-to-air fighter planes. The Israeli Air Force has obviously developed some kind of precision bombing equipment for these aircraft, however, as they were used to strike Palestine Liberation Organization headquarters in Tunis in 1985. Christopher to aid talks

Meanwhile, the US has also inserted itself back into the diplomatic track of Middle East peace efforts with Secretary of State Warren Christopher's announced trip to the region next month.

He will shuttle about in an attempt to help Israel and the PLO settle differences over peace-accord implementation. Negotiators are continuing to squabble, for instance, over the geographical boundaries of the prospective Palestinian-run town of Jericho, and over the size of Israeli forces that will be left in Gaza to protect Jewish settlers there. At Israel's request, he will also try to break the talk impasse between Israel and Syria over the Golan Heights.

The Golan Heights, captured by Israel in the 1967 war, remains a buffer zone between nations that are still bitter adversaries. Currently, Israel and Syria are locked in a kind of Alphonse-and-Gaston ``you go first ... no, you go'' dance over the strategic area. Israel says it will talk about giving up the Golan, or, at least, parts of it, when Syria indicates a desire for comprehensive peace. Syria, for its part, says it will talk about peace after it is clear that Israel will give up the Golan.

Syria has rejected an Israeli offer of secret talks, Rabin said during his Washington visit. An official Syrian newspaper also blasted the Israeli-PLO peace Nov. 15, saying Palestinians, in fact, have gained nothing.